On the drag reduction effect and shear stability of improved acrylamide copolymers for enhanced hydraulic fracturing

Polymeric drag reducers, such as partially hydrolysed polyacrylamide (PHPAAm), are important chemical additives in hydraulic fracturing fluids as they can significantly decrease the frictional pressure drop in the casing (by up to 80%), resulting in an increase of the injection rate that can be delivered to the fracturing point. The incorporation of sodium 2-acrylamido-2-methylpropane sulphonic acid (NaAMPS) moieties into polyacrylamide (PAAm) can further improve the performance of fracturing fluids by addressing some compatibility issues related to the use of PHPAAm, e.g., the sensitivity to water salinity. In this study, three types of poly(acrylamide-co-NaAMPS) and pure PHPAAm were investigated with respect to polymer induced drag reduction and mechanical polymer degradation in turbulent pipe flow in a pressure-driven pipe flow facility. The test section comprised a horizontal 1" bore circular cross-section pipe. The facility was modified in order to allow long time/length experiments by automatically recirculating the polymer solution in a closed-loop through the test section. The presence of NaAMPS groups in the copolymer backbone is found to increase the ability of PHPAAm to reduce frictional drag while the vulnerability to mechanical degradation remains unaffected. The drag reduction of NaAMPS copolymer solutions can be described by a modified version of Virk׳s correlation (1967), extended to include the effect of Reynolds number. Polymer mechanical degradation is found to proceed until the friction reducer is almost ineffective in reducing drag. This phenomenon is in contrast with the most common correlation for polymer degradation, which predicts the existence of an asymptotic (but finite) limit to the reduced drag reduction.